1. Field of the Invention
The invention relates to an ink ejecting printer having maintenance means for maintaining an ink ejecting head used in the printer.
2. Description of the Related Art
There exist ink ejecting printers having maintenance means for maintaining the ink ejecting head. A typical example of the maintenance means is a wiping member that slides over the nozzle surface of the head to wipe paper powder, dust or ink of increased viscosity therefrom. Another typical maintenance means constitutes suction means for sucking excess ink from the nozzle surface of the head, or forced discharging means for forcibly discharging ink from inside the head, whereby the impurities and air bubbles within the head are discharged therefrom along with a small amount of ink. Many of the recently introduced ink ejecting printers combine these two maintenance means, i.e., the wiping means and the suction or forced discharging means.
With the above ink ejecting printers, a head maintenance operation is carried out at intervals based upon predetermined parameters (for example, operation time, number of characters printed, number of dots printed, and/or number of pages printed). Illustratively, some conventional ink ejecting printers switch their timing for wiping from a predetermined period of operation performed to the predetermined number of dots to be printed, as disclosed in Japanese Unexamined Patent Publications Nos. 2-141248 and 3-5154.
Because the printers are expected always to provide printing of high quality, certain reductions in printing speed are bound to occur regardless of the timing of head maintenance. Illustratively, there are two major modes in which ink ejecting printers are used: one in which the printer prints on a draft, or lower quality, basis the documents prepared typically by a host computer, and the other in which the printer makes a high quality print of what was printed on the draft basis, edited accordingly, and finalized. For draft printing, what many of today's users typically want is primarily rapid printing at the expense of somewhat reduced levels of printing quality. The requirement for rapid printing is met by ink ejecting printers that permit selection of either normal print mode where desired image patterns are printed unmodified, or thin-out mode where the image patterns are thinned out before being printed. With the quality of printing reduced, the thin-out mode nevertheless offers the advantage of lower ink consumption and a boost in printing speed.
The above ink ejecting printers with two modes, when equipped with the head maintenance function, have one disadvantage. That is, the timing of head maintenance using the head maintenance function in thin-out mode is the same as in the normal print mode. Users having selected thin-out mode for trial printing are often disappointed to see the speed of printing not increased as significantly as they hoped would be the case.
Further, some conventional ink ejecting printers have a water repellent layer formed over the nozzle surface to prevent the retention of excess ink thereon in order to enhance the linearity of ejected ink drops. In particular, many recently developed ink ejecting printers combine the wiping means with the water repellent layer to achieve higher levels of printing quality. In such printers, however, those that perform wiping both in the draft print mode and in the normal print mode tend to suffer from a shorter service life of their print head. This is because every time the nozzle surface is wiped, a bit of the water repellent layer is peeled therefrom.